This invention relates to a motor vehicle axle assembly and in particular to a rear axle utilizing a wheel end axial retention system.
In rear wheel drive motor vehicles with rigid rear axles it is conventional practice to provide a pair of solid axle shafts extending from the differential outboard to the rear driven wheels. In such designs, a pair of rigid axle tubes extend outboard from the differential with brake components mounted to the ends of the tubes. The solid axle shafts rotate within the axle tubes. The inboard end of each axle shaft is splined and has a circumferential end groove. The opposite axle shaft end (i.e. the "wheel end") features a wheel mounting flange having wheel mounting studs. At the wheel end the axle shaft is supported by a roller bearings unit positioned at the end of the axle tube. Lubrication of the bearing is provided by axle lubricant present within the axle tube. The outboard bearing restrains the axle radially but does not provide axial or thrust support. The axle shaft is retained axially through a C-washer or snap ring installed in the groove at the inboard end of the axle shaft after the shaft end is passed through a differential bevel gear.
Certain disadvantages are inherent in the above described axle design. This method of axial retention allows a considerable axle shaft end play (i.e. axial "run-out" or motion). This end play can adversely affect the performance of a rear disk brake due to caliper "knock back" and can further produce a noticeable "clunk" in cornering maneuvers as the lateral acceleration forces (i.e. axial axle forces) are reversed. In addition, the axle shaft end play can make discrete mounted rotation speed sensors used in anti-lock braking systems (ABS) difficult to incorporate due to a time-varying air gap between the sensor and the associated rotating tone wheel or exciter.
In addition to performance concerns the above described axle design approach further complicates the process of axle shaft removal since an inspection cover of the differential must typically be removed and the differential lube drained in order to provide access to the axial retention device. Once the retainer is removed the axle can be laterally withdrawn. However, the roller bearing assembly which is typically press fit onto a machined diameter at the axle shaft outboard end must be pressed off after removing a bearing retainer ring (often destroyed in the process).
In accordance with the present invention, a novel approach toward rear axle bearing retention and axial restraint is provided. Through this design, axial end play is significantly reduced providing advantages for rear disk brake applications. In addition, due to a reduced end play, the use of ABS sensors is accommodated. This approach also makes use of new generation unit bearings which are permanently lubricated. And finally, the process of rear axle and bearing disassembly is simplified as compared with current design approaches.
An axle assembly of this invention incorporates a cartridge bearing assembly located at the outboard end of the axle shaft having an outer race which is trapped between the axle tube and a brake caliper bracket/bearing carrier element which is bolted or otherwise fastened to the axle tube. The inner race of the cartridge bearing is trapped between the axle wheel mounting flange at the outboard end of the axle and a threaded nut which meshes with threads formed on the axle shaft. With this system all of the structures which provide lateral restraint for the axle are located at the outboard or wheel end of the axle. Through the use of precision machined surfaces and a threaded nut for clamping the bearing inner race, lateral end play of the axle shaft can be reduced significantly.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.